Inheritance of Cry1F resistance in fall armyworm (Spodoptera frugiperda)

To assess the genetic basis of Cry1F resistance in fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), pupae of a Cry1F-susceptible population (SS) and two Cry1F-resistant populations isolated from field collections in Puerto Rico (RR-PR) and Florida (RR-FL) were divided by gender before eclosion. Reciprocal parental crosses were conducted to generate four F1 hybrid populations. Two trials were conducted to assay the Cry1F susceptibility of offspring (newly-hatched larvae) of the three parent and four F1 populations based on 7-d mortality on leaf tissue excised from greenhouse gown non-Bt and Cry1F corn at V5-V8 plant stages. Results of the two trials were consistent. The laboratory bioassay showed that both RR-PR and RR-FL were highly resistant to Cry1F corn leaf tissue, while the SS population was susceptible. Mortality on Cry1F corn leaf tissue varied among the four F1hybrid populations, suggesting the Cry1F resistance in FAW might not be autosomal. Effective dominance level, DML, measured based on the 7-d mortality ranged from 0.21 to 0.98, indicating that the Cry1F resistance in FAW was incompletely recessive to dominant on leaf tissue of Cry1F corn.